The present invention relates to a semiconductor integrated circuit device for a display controller, having therein a RAM (Random Access Memory) for storing display data and controlling a display device, and relates to a technique effectively used for, for example, a liquid crystal display controller driver for driving a liquid crystal display panel.
In recent years, as a display device of a portable electronic device such as a cellular phone or a PDA (Personal Digital Assistant), generally, a dot-matrix-type liquid crystal panel in which a plurality of display pixels are arranged two-dimensionally in a matrix is used. The device has therein a liquid crystal display (LCD) controller (liquid crystal controller) formed as a semiconductor integrated circuit for performing a display control of the liquid crystal panel and a liquid crystal driver for driving the liquid crystal panel under control of the controller, or a liquid crystal display controller driver (liquid crystal controller driver) having therein the liquid crystal controller and the liquid crystal driver.
Hitherto, a liquid crystal display controller driver (including the liquid crystal controller) has therein a RAM for storing display data in a chip. The storage capacity of the built-in RAM is generally determined according to the size of a display screen of the liquid crystal panel to be driven. As compared with a general memory, the storage capacity of the RAM is smaller, and a so-called redundancy circuit for repairing a defective bit is not provided.
The storage capacity of the built-in RAM is specified to the size of the screen of the liquid crystal panel for the following reason. In the liquid crystal controller driver, even when the capacity of the built-in RAM is set to the size of storing display data of one screen of the liquid crystal panel, since the proportion of the RAM occupying the chip area is relatively large, increase in the storage capacity directly results in increase in the chip cost. With respect to a built-in RAM having the capacity of storing display data of one screen, decrease in the yield due to a defect in the RAM is not a big issue, so that there is little necessity to provide a redundancy circuit. Increase in the chip size by providing a redundancy circuit can be avoided.
For example, Japanese Unexamined Patent Publication No. 2000-347646 discloses that the storage capacity of a built-in RAM in a liquid crystal controller driver is set to the size of storing display data of one screen of a liquid crystal panel.